As it is well known in the art, a vector is a tool that allows or facilitates the transfer of an entity from one environment to another. By way of example, some vectors used in recombinant DNA techniques allow entities—such as a segment of DNA (such as a heterologous DNA segment, such as a heterologous cDNA segment)—to be transferred into a target cell. Optionally, once within the target cell, the vector may then serve to maintain the heterologous DNA within the cell or may act as a unit of DNA replication. Examples of vectors used in recombinant DNA techniques include plasmids, chromosomes, artificial chromosomes or viruses.
Thus, vectors can be used to deliver proteins and/or nucleotide sequences to targeted cells, such as tumour cells.
However, as it is well known, nucleotide sequences and proteins are complex molecules which may be produced from biological sources, most usually from genetically engineered organisms or cell cultures. Furthermore, the procedures for the production of nucleotide sequences and proteins can be complicated, labour intensive and costly. Furthermore, pharmacological properties and other aspects of the function of some proteins—such as immunoglobulins derived from non-human biological sources—and nucleotide sequences may frequently differ in important ways from the activity of the corresponding natural human immunoglobulins produced in human cells. By way of background information, an immunoglobulin is a member of a family of related multimeric proteins which are normally secreted from cells of the B-lymphocyte lineage of a vertebrate, whose typical function is to bind specifically with a region of a macromolecule identified as non-self. Immunoglobulins represent a major component of the immune response repertoire of the organism and are synonymous with “antibodies”.
One major cause of such differences in activity may be due to variations in the pattern of glycosylation of proteins derived from different species (reviewed in Bebbington 1995; In Monoclonal Antibodies: the second generation ed. H. Zola pg 165-181). Furthermore, systemic administration of proteins (especially those containing toxin domains) and nucleotide sequences can induce additional pharmacokinetic and toxicological problems (reviewed in Scheinberg and Chapman 1995. In Monoclonal antibodies (ed. Birch and Lennox) Chapter 2.1).